Groundwater Modeling Used to Design of a Tailings Impoundment Removal near Yellowstone National Park

Tom Henderson, Montana DEQ Mike Boduin, PE Pioneer Technical Services April 13, 2017 YNP

McLaren Mill and Tailings McLaren Mill and Tailings and National Park Service Concerns • 1933 – 1953: Approximately 250,000 yd3 tailings in floodplain • Memos to Chief Ranger describe annual inspections – water below Mill ‘milky’ in July and August – settling pond dyke ‘leaking badly’ (16 Jun 1949) – section of settling pond earthen wall ‘washed out during heavy rain’ (27 Jun 1950) • Mines ‘adversely affected the McLaren Gold Mine Mill, 1946. Courtesy of Cooke City Montana Museum. fish producing capacity of SBC’ (Mills 1968)

Soda Butte Creek Below Tailings Pre-reclamation

Tailings Discharges (USGS): Fe 418 mg/L Al 122 mg/L Cu 6 mg/L Pb 0.6 mg/L Cd 0.06 mg/L

Approximate Annual Loads: 40,000 lb Fe 12,000 lb Al 590 lb Cu 58 lb Pb 6 lb Cd

Tailings Dam Cross-Section

1969 soil cap 1990s work to stabilize dam toe

7640

Multiple seeps of 7630 contaminated Tailings ? water 7620 Silty sands

7610 Silty clays

7600 Sands with silts, gravels and

Elevation in Feet cobbles

7590

7580 0 85 Horizontal Distance in Feet Targeted Load Reductions

MT DEQ 2002 – ‘Given the high iron loading from the McLaren Tailings, it is assumed that at least a 99% reduction in total load for iron will be needed to satisfy iron loading allocation…this 99% load reduction will likely be similar for copper, manganese, and Yashan et al. 2002. Water Quality Restoration Plan for the Cooke City TMDL other metals.’ Planning Area. Montana Department of Environmental Quality. Helena, Montana. 208 pp. Published September 23, 2002. New World Mining District

7 Climate at 7700 Feet AMSL

Spring Fall

Tailings Impoundment

∆

Artesian GWArtesian Ag, As, Cd, Cu, Fe, Pb, Zn 10 - 1000x Montana standards ~1 - 5 million gallons

Tailings Stabilization (?) Design Investigations

Pumping well

May 22, 2009 Groundwater System

2 Ft Soil Cap

∆

20-35 Ft Tailings ∆

5 – 50 Ft Alluvial Aquifer

Granitic Bedrock Seasonal Variability

7650

7645 Ground elevation Soil cap 7640 Tailings

7635 Tailings water level Elevation (ft AMSL) 7630 Aquifer water level 7625 May 28-Jul 27-Jul 2009 28-Apr 30-Oct 28-Jun 28-Jan 27-Jun 27-Feb 29-Mar 29-Nov 27-Aug 30-Sep 29-Dec 29-May 28-May

2009 2010 Pump Testing and Analysis

0. Obs. Wells Response in unpumped PZ-04S Aquifer Model tailings impoundment Leaky Solution 0.1 Q = 15 gpm Neuman-Witherspoon Parameters T = 1438.4 ft2/day S = 0.006489 r/B = 0.05623 0.2 ß = 0.01862 T2 = 0.07217 ft2/day S2 = 0.1259

Displacement (ft) 0.3

0.4

0.5 0. 600. 1.2E+3 1.8E+3 2.4E+3 3.0E+3 Time (min) MODFLOW Modeling Model Calibration

Figure E-8: Groundwater Head Calibration Modeling Results

• Approximately 800 GPM extraction rate required to drop water table to base of tailings impoundment • Winter pumping desirable to dampen spring surge • Additional pumping under the tailings required during the summer

Tailings Excavation

Photo taken July 11, 2012

ContinuedTailings Excavation Pumping Tailings (~500,00 Tons) Stabilized & Excavated

Static Groundwater Level

Photo taken August 15, 2012 Water Balance

Treated Water (~300 GPM) Soda Butte Creek2008 September 2008 Soda Butte Creek2013 July 2013 2016

26

Basin Assessment

Yellowstone National Park - Water Quality Assessment - Reevalution of Impairments to Soda Butte Creek

May 2016 SBC WQ Study 2015 & 2016

Cooke City MC SBC-2: Water Quality vs. DEQ-7 Standards

April 14 USFS 2000 – 2010 June 28 2000 July 7 July 15 October 10 31 Sampling Events April 19 20 Iron exceedances 2015 August 4 2001 June 25 8 Copper exceedances September 9 October 12 October 21 April 22 1 Lead exceedance 2002 July 1 November 18 October 9 April 25 April 23 DEQ/NPS 2015 – 2016 May 17 2003 June 30 2016 June 2 September 30 11 Sampling Events April 7 0 Iron exceedances June 13 2004 June 30 1 Copper exceedance June 28 October 7 April 4 0 Lead exceedance 2005 June 27 September 28 April 26 2006 June 26 September 25 April 12 2007 June 14 September 19 April 15 2008 July 16 September 23 April 9 2009 June 22 SBC-2 is located downstream of the McLaren Tailings project September 29 31 2010 April 6 McLaren Tailings reclamation project began June 2010 SBC WQ Study 2015 & 2016 Sample Results

• Cu levels in SBC variable but mostly below MT criterion • Exception is Miller Creek where [Cu] are 2 to 3X higher • At YNP boundary Cu below WQ Standards

Direction of Flow SBC WQ Study 2015 & 2016 Sample Results

• Fe levels lowest below former tailings site • Highest [Fe] from two tributaries • At YNP boundary generally below MT DEQ chronic aquatic life criterion Direction of Flow SBC-4: Water Quality vs. DEQ-7 Standards

April 14 USFS 2000 – 2010 June 28 2000 July 7 October 10 31 Sampling Events July 15 April 19 6 Iron exceedances 2015 August 4 2001 June 25 September 9 October 12 3 Copper exceedances October 21 April 24 4 Lead exceedances 2002 July 1 November 18 October 8 April 25 April 22 DEQ/NPS 2015 – 2016 May 17 2003 July 2 September 30 11 Sampling Events 2016 June 2 April 8 2 Iron exceedances June 13 2004 June 30 June 28 October 7 0 Copper exceedances April 4 0 Lead exceedances 2005 June 27 September 28 April 26 2006 June 26 September 25 April 12 2007 June 14 September 19 April 15 2008 July 16 September 23 April 9 2009 June 22 September 29 34 2010 April 6 SBC-4 is located upstream of YNP northeast entrance station SBC WQ Study 2015 & 2016

Not Sampled

Meets Standard

Exceeds Standard Resource Restoration

Yellowstone Cutthroat Trout Conservation - Montana Fish, Wildlife & Parks - Wyoming Department of Game and Fish - National Park Service - Custer Gallatin National Forest - Shoshone National Forest Summary

• Montana is evaluating delisting of metals impairments to Soda Butte Creek • Reclamation project is a milestone for the Greater Yellowstone ecosystem • Design investigations critical to project success • Support provided by OSMRE throughout project design and reclamation

Questions